Diagnosis of Bovine TB in Ghana

The isolation of viable mycobacteria by culture and their identification is the laboratory diagnostic method accepted globally as the gold standard for confirming the diagnosis of tuberculosis in various species (Asante-Poku et al.

Diagnostic specimens for culture are often collected from lesions in lymph nodes and parenchymatous organs such as the lungs, liver, and spleen (Dungworth 1993). However, this is not routinely done in Ghana due to the lack of the required diagnostic infrastructure of the Ghanaian Veterinary Services Department (VSD), though such facilities are available in some research centers in the country. Thus, to the best of our knowledge, only few research studies have tried to isolate mycobacteria for identification from suspected lesions to confirm BTB. Direct microscopic smear examination for acid-fast bacilli (AFB) after staining with carbol fuchsin is simple and routinely used for the diagnosis of human TB (Forrellad et al.

2013). However, it is rarely used for BTB due to its low sensitivity, as it requires a concentration of 10⁴ bacilli per milliliter suspension to give a positive smear test (Asante-Poku et al. 2014; Allen and Mitchison 1992; Pearson et al. 2008). In addition, this method lacks specificity, as it cannot differentiate between the various mycobacterial species. The standard Single Intradermal Cervical Test (SIT) with purified protein derivative (PPD) tuberculin for detection of infection in live cattle (Pearson et al. 2008) is available, but it is not used routinely due to logistical constraints. The main routine method for diagnosing BTB in Ghana is a macroscopic inspection done at various abattoirs to detect lesions in carcasses (Menzies 2000). This method, though it may not be sensitive, offers the opportunity for targeted screening of tuberculous carcasses to protect the consumers’ health. It also remains the only viable surveillance regimen for the VSD to establish the geographic extent of the disease within different geographical areas in the country. The Ghanaian VSD has not yet developed the capacity to do the interferon gamma assays that are available (Rothel et al. 1990; Neill and Pollock 2000). Molecular detection methods such as polymerase chain reaction (PCR) and other genotyping methods are also not routinely used due to the cost and lack of infrastructure. Nevertheless, several in-country research studies have used PCR-based methods to characterize mycobac­terial isolates from both humans and animal sources. In Ghana, these molecular techniques are increasingly being applied primarily to enhance detection, and for the typing of mycobacteria (Bonsu et al. 2000).

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